Shimano M485 piston un-stucker

My Shimano M485 had one of the pistons quite stuck, which resulted in one of the brake pads being completely worn out rather quickly.

I used this to keep the other piston (the one that still moved) in place and to then exert pressure on the one that was stuck. It didn't take much effort to get it un-stuck, but it will still need some further work to get back to being smooth.

At least on M485 the pistons are not right in the middle of the brake pads so the space for the piston is a bit too